Acute spontaneous subdural hematoma of arterial origin is very rare. We report five patients who presented with a history of sudden onset of severe headache and vomiting and who developed progressive neurologic deficits, three becoming comatose. The symptomatologic onset was indistinguishable from other cerebrovascular disorders; none of the patients had a history of head trauma. In all our patients, the source of bleeding was identified at operation as a cortical artery located near the Sylvian region. Comparable cases in the literature are reviewed and the etiologic possibilities are discussed.